Create basic chatbot

app.py

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+from langchain.callbacks.base import BaseCallbackHandler
+from langchain.schema import ChatMessage
+from langchain_openai import ChatOpenAI
+import streamlit as st
+
+st.set_page_config(page_title="Streamlit + Langchain")
+
+st.title("Basic Chatbot with Streamlit and Langchain")
+st.caption("Features text streaming")
+
+
+class StreamHandler(BaseCallbackHandler):
+    def __init__(self, container, text=""):
+        self.container = container
+        self.text = text
+
+    def on_llm_new_token(self, token: str, **kwargs) -> None:
+        self.text += token
+        self.container.markdown(self.text)
+
+
+# Text input to enter OpenAI API key
+with st.sidebar:
+    OPENAI_API_KEY = st.text_input("Enter your OpenAI API Key", type="password")
+
+# Streamlit session state
+if "messages" not in st.session_state:
+    st.session_state["messages"] = [
+        ChatMessage(role="assistant", content="How can I help you?")
+    ]
+# Display all chat messages from session state
+for message in st.session_state.messages:
+    st.chat_message(message.role).write(message.content)
+# If user submits a prompt in the text input, continue
+if prompt := st.chat_input():
+    if not OPENAI_API_KEY:
+        st.error("Please add your OpenAI API key to continue.")
+        st.stop()
+    # Add user's prompt to the chat messages
+    st.session_state.messages.append(ChatMessage(role="user", content=prompt))
+    st.chat_message("user").write(prompt)
+    # Display the assistant's response with langchain query
+    with st.chat_message("assistant"):
+        stream_handler = StreamHandler(st.empty())
+        llm = ChatOpenAI(
+            model="gpt-4o-mini",
+            openai_api_key=OPENAI_API_KEY,
+            streaming=True,
+            callbacks=[stream_handler],
+        )
+        response = llm.invoke(st.session_state.messages)
+        st.session_state.messages.append(
+            ChatMessage(role="assistant", content=response.content)
+        )

requirements.txt

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+streamlit
+langchain
+langchain-openai